The present invention relates to a setting method of an optimum number of teeth of each helical gear of a helical gear pair and the helical gear pair whose numbers of teeth are set according to the setting method.
Recently, a performance requirement for a gear sound (gear noise) in an automotive vehicle tends to become more strict year by year. Especially, the gear noise catches human's ears due to its dull sound. Thus, a specification requirement of the noise in the gear mounted in the vehicle tends to become more strict year by year. A gear noise performance is, as different from dynamic performances of other mechanical elements, largely dependent upon not only a gear design but also a gear manufacturing method or a working accuracy (a manufacturing quality) and is dependent upon a passenger compartment environment during a driving of the gear.
As a gear noise countermeasure to cope with an industrial demand such as described above, a rib reinforcement into a gear case (box) and an addition of a shielded material or mass onto a vehicle body are generally carried out so that the countermeasures to suppress vibrations of a surrounding member due to an exciting force of the gear and to suppress a transmission of the developed gear sound. In recent years, a robust gear design with a manufacturing error developed during a manufacturing process of the gear taken into consideration is carried out to make an influence of a tooth flank error variation on a transmission error of gears (meshing error) dull and to add a gear finishing process after a heat treatment. Thus, the gear sound (noise) itself is reduced. These countermeasures are described in a Japanese thesis of a degree of Kyoto University titled Method of Both Optimum Design in Vibration and Strength of Power Transmission Involute Cylindrical Gear authored by Masaharu Komori in 2002, SAE Paper 1999011053 (a study on Optimum Tooth Modifications of Helical Gears under Various Loads) in 1999 by Hiroki MAKI, and a paper series C (volume No. 66, 646 (2000-6) No. 99-1497) of the Japan Society of Mechanical Engineers by Masaharu KOMORI et al in 1959.